diff --git a/nmt.go b/nmt.go
index 9f52d03..63a2e13 100644
--- a/nmt.go
+++ b/nmt.go
@@ -143,7 +143,7 @@ func New(h hash.Hash, setters ...Option) *NamespacedMerkleTree {
 // Prove returns a NMT inclusion proof for the leaf at the supplied index. Note
 // this is not really NMT specific but the tree supports inclusions proofs like
 // any vanilla Merkle tree. Prove is a thin wrapper around the ProveRange.
-// If the supplied index is invalid i.e., if index < 0 or index > len(n.leaves), then Prove returns an ErrInvalidRange error. Any other errors rather than this are irrecoverable and indicate an illegal state of the tree (n).
+// If the supplied index is invalid i.e., if index < 0 or index > n.Size(), then Prove returns an ErrInvalidRange error. Any other errors rather than this are irrecoverable and indicate an illegal state of the tree (n).
 func (n *NamespacedMerkleTree) Prove(index int) (Proof, error) {
 	return n.ProveRange(index, index+1)
 }
@@ -164,7 +164,7 @@ func (n *NamespacedMerkleTree) Prove(index int) (Proof, error) {
 // generated using a modified version of the namespace hash with a custom
 // namespace ID range calculation. For more information on this, please refer to
 // the HashNode method in the Hasher.
-// If the supplied (start, end) range is invalid i.e., if start < 0 or end > len(n.leafHashes) or start >= end,
+// If the supplied (start, end) range is invalid i.e., if start < 0 or end > n.Size() or start >= end,
 // then ProveRange returns an ErrInvalidRange error. Any errors rather than ErrInvalidRange are irrecoverable and indicate an illegal state of the tree (n).
 func (n *NamespacedMerkleTree) ProveRange(start, end int) (Proof, error) {
 	isMaxNsIgnored := n.treeHasher.IsMaxNamespaceIDIgnored()
@@ -248,7 +248,7 @@ func (n *NamespacedMerkleTree) ProveNamespace(nID namespace.ID) (Proof, error) {
 // validateRange validates the range [start, end) against the size of the tree.
 // start is inclusive and end is non-inclusive.
 func (n *NamespacedMerkleTree) validateRange(start, end int) error {
-	if start < 0 || start >= end || end > len(n.leaves) {
+	if start < 0 || start >= end || end > n.Size() {
 		return ErrInvalidRange
 	}
 	return nil
@@ -268,12 +268,12 @@ func (n *NamespacedMerkleTree) buildRangeProof(proofStart, proofEnd int) ([][]by
 	}
 
 	// start, end are indices of leaves in the tree hence they should be within
-	// the size of the tree i.e., less than or equal to the len(n.leaves)
+	// the size of the tree i.e., less than or equal to n.Size()
 	// includeNode indicates whether the hash of the current subtree (covering
 	// the supplied range i.e., [start, end)) or one of its constituent subtrees
 	// should be part of the proof
 	recurse = func(start, end int, includeNode bool) ([]byte, error) {
-		if start >= len(n.leafHashes) {
+		if start >= n.Size() {
 			return nil, nil
 		}
 
@@ -341,7 +341,7 @@ func (n *NamespacedMerkleTree) buildRangeProof(proofStart, proofEnd int) ([][]by
 		return hash, nil
 	}
 
-	fullTreeSize := getSplitPoint(len(n.leafHashes)) * 2
+	fullTreeSize := getSplitPoint(n.Size()) * 2
 	if fullTreeSize < 1 {
 		fullTreeSize = 1
 	}
@@ -449,7 +449,7 @@ func (n *NamespacedMerkleTree) Push(namespacedData namespace.PrefixedData) error
 // Any error returned by this method is irrecoverable and indicate an illegal state of the tree (n).
 func (n *NamespacedMerkleTree) Root() ([]byte, error) {
 	if n.rawRoot == nil {
-		res, err := n.computeRoot(0, len(n.leaves))
+		res, err := n.computeRoot(0, n.Size())
 		if err != nil {
 			return nil, err // this should never happen since leaves are validated in the Push method
 		}
@@ -484,7 +484,7 @@ func (n *NamespacedMerkleTree) MaxNamespace() (namespace.ID, error) {
 func (n *NamespacedMerkleTree) computeRoot(start, end int) ([]byte, error) {
 	// in computeRoot, start may be equal to end which indicates an empty tree hence empty root.
 	// Due to this, we need to perform custom range check instead of using validateRange() in which start=end is considered invalid.
-	if start < 0 || start > end || end > len(n.leaves) {
+	if start < 0 || start > end || end > n.Size() {
 		return nil, fmt.Errorf("failed to compute root [%d, %d): %w", start, end, ErrInvalidRange)
 	}
 	switch end - start {
@@ -533,8 +533,8 @@ func getSplitPoint(length int) int {
 }
 
 func (n *NamespacedMerkleTree) updateNamespaceRanges() {
-	if len(n.leaves) > 0 {
-		lastIndex := len(n.leaves) - 1
+	if n.Size() > 0 {
+		lastIndex := n.Size() - 1
 		lastPushed := n.leaves[lastIndex]
 		lastNsStr := string(lastPushed[:n.treeHasher.NamespaceSize()])
 		lastRange, found := n.namespaceRanges[lastNsStr]
@@ -570,7 +570,7 @@ func (n *NamespacedMerkleTree) validateAndExtractNamespace(ndata namespace.Prefi
 	nID := namespace.ID(ndata[:n.NamespaceSize()])
 	// ensure pushed data doesn't have a smaller namespace than the previous
 	// one:
-	curSize := len(n.leaves)
+	curSize := n.Size()
 	if curSize > 0 {
 		if nID.Less(n.leaves[curSize-1][:nidSize]) {
 			return nil, fmt.Errorf(
@@ -615,3 +615,8 @@ func MaxNamespace(hash []byte, size namespace.IDSize) []byte {
 	max := make([]byte, 0, size)
 	return append(max, hash[size:size*2]...)
 }
+
+// Size returns the number of leaves in the tree.
+func (n *NamespacedMerkleTree) Size() int {
+	return len(n.leaves)
+}